Current studies in progress pertain to the further definition of the heavy and light chain types of immunoglobulin molecules which can be synthesized by an individual clone of antibody producing lymphocytes. The approach to this problem has been confined thus far to the study of a select group of patients with malignant lymphoproliferative disorders who have evidence of more than one type of paraprotein in their sera. The nature of the specific investigation includes a comparative analysis of the unique V-region idiotypic antigenic determinants expressed by the individual serum paraproteins, a comparison of pertinent aspects of the aminoacid sequences of the VH and VL regions of the separate paraproteins, and studies on the capacity of individual homologous lymphocytes to produce the distinct serum paraproteins.